Optical module, method for manufacturing optical module and optical communication apparatus

ABSTRACT

The present invention is to reduce the package cost and secure the high reliability in an optical module having an optical device and an optical fiber.  
     In the case where the optical module is constituted by use of a pre-molded plastic package, a molding resin is flown parallely with the optical axis direction of the optical fiber on which the plastic package is formed by injection molding. Further, in the case where the plastic package is formed by the comprehensive molding, the flowing direction of resin is parallel with the optical axis direction of the optical fiber to be installed. In the case where a resin case is used, the package exhibits the high rigidity and low thermal expansion properties in connection with the flowing direction of resin, thus reducing the external stress and thermal stress applied to the optical fiber. Accordingly, the high reliability is secured. In the case of the comprehensive molding, the molding pressure applied to the optical fiber is reduced. Therefore, the high reliability is secured.

TECHNICAL FIELD

[0001] The present invention relates to a resin molding type opticalmodule having an optical device and an optical fiber packaged with aresin, an optical fiber communication apparatus using the resin moldingtype optical module, and an optical communication system.

BACKGROUND ART

[0002] Recently, great demands for lowering the cost of the opticalmodule have been made in order to introduce the optical fibercommunication system into the subscriber network system on a full scale.From a viewpoint of this, with respect to the packaging technology, aresin sealing method (a plastic package method) is influential in placeof a hermetic sealing method for a metallized package or a ceramicpackage which has heretofore occupied the mainstream in the field ofoptical devices. This is because the resin sealing method is suitablefor mass- and inexpensive production.

[0003] In the past, in the field of general semiconductor devices suchas LSI and hybrid IC, the following various methods have been known asresin sealing methods. (1) a transfer molding method (a method forcompressing preheated powdery resin to transfer it to a mold), (2) acasting injection method (method for injecting a liquid resin into amold frame), (3) a potting injection method (a method for injecting aliquid resin into a resin case), (4) a cap sealing method (a method foradhering a cap to a hollow case with resin), (5) a dipping method (amethod for dipping an element into a resin liquid vessel), and (6) adropping method (a method for dropping a liquid resin onto an element).

[0004] Further, the following examples in which the aforementioned resinsealing methods are applied to the optical module have been known. Forexample, there are Japanese Patent Application Laid-Open No. 2-271308(Article 1), Japanese Patent Application Laid-Open No. 1-304405 (Article2), Japanese Patent Application Laid-Open No. 7-321407 (Article 3),Proceedings of the Conference of the Institute of Electronics,Information and Communication Engineers in 1996, SeparateVolume—Electronics 1, pages 478 to 479 (Article 4), the same collection,page 216 (Article 5), and the same collection, page 207 (Article 6).

[0005] Article 1: In the receptacle type optical module for fiber optictransmission, a hermetic seal by way of a metallized package and a resinseal by way of transfer molding are jointly used. A laser diode and aphotodiode are once hermetically sealed in a can type metallizedpackage, and the can type metallized package is molded by the transfermolding method together with electronic circuit parts and a lead frame.

[0006] Article 2: In the receptacle type module, a potting injectiontype method is used. A resin case comprises a black epoxy resin moldedarticle. A cylindrical receptacle is provided in part thereof. A lightemitting diode and a light receiving diode are installed on a leadframe, and are received in the resin case. The resin case are filledwith transparent epoxy resins by potting. The light emitting diode orthe light receiving diode is directly sealed by the transparent resin.

[0007] Article 3: This is concerned with a pickup light source of anoptical disk. In this example, a casting injection method (or a transfermolding method) and a resin sealing method by way of a dropping methodare jointly used. The laser diode is fixedly secured to the lead framethrough a heat sink, and these are sealed by casting of transparentepoxy resins. A silicone resin is coated on the surface of the laserdiode by the dropping method in order to prevent the optical damage ofthe sealed resin caused by emitting light of laser and the peeling of aninterface between the laser diode and the sealed resin.

[0008] Article 4: In the pigtail type module for fiber optictransmission, a casting injection method is employed. In this example,the laser diode and the bare portion of the pigtail fiber are sealedwith resin. That is, the laser diode and the extreme end of the barefiber are secured to the heat sink, and the heat sink is fixedly securedto the metallic stem. They are molded by casting of transparent epoxyresins. The jacket portion of the pigtail fiber is not sealed withresin.

[0009] Article 5: In the pigtail type module, a hollow resin case isclosed by a cap sealing method. The laser diode and the bare portion ofthe pigtail fibers are secured to a silicon base plate, and the baseplate and the jacket portion are secured to the resin case. A lead frameis insert-molded in the resin case. The bare fiber and the base plate,the jacket and the resin case, and the cap and the resin case are bondedone another by ultraviolet setting resins.

[0010] Article 6: In the receptacle type module, the cap sealing methodand the transfer molding method are jointly used. A laser diode, theextreme end of a ferrule with fiber, and a lead frame are secured to asilicon substrate to constitute a substrate assembly. The laser diodeand the ferrule are once sealed by adhering a silicon cap on thesubstrate with the epoxy resin, and the substrate assembly is sealed bythe transfer molding of black epoxy resins except the rear end of theferrule and the outer lead portion of the lead frame. The receptacle isconstituted by a part of the transfer molded article, the rear end ofthe ferrule and a housing provided by other parts.

[0011] The plastic package is influential for lowering the cost of theoptical module as compared with the metallized package or the ceramicpackage, but has difficulties such that generally, the moisturepermeability is high, and the coefficient of thermal expansion is large.These factors synthetically lower the reliability of the plasticpackage. It is therefore important, for putting the plastic module inpractical use, how to secure the reliability while making use of themerit of lowering the cost of the plastic package.

[0012] It is concretely necessary to make consideration relative to theaforementioned problems from the following two aspects. First, themoisture resistance should be increased in respect of constituent partsof the module such as an optical device, an optical fiber, a base plateand so on. Secondly, with respect to the optical coupling between theoptical device and the optical fiber, it is necessary to suppressextremely highly a deviation in position caused by the thermal stress,the external force, the molding pressure, etc. In particular, in thesemiconductor laser module, a demand relative to such a position issevere. This is because the spot size of the laser diode is smaller thanthe spot size of the light emitting diode and the light receivingdiameter of the photodiode.

[0013] Any of the aforementioned prior arts have both merits anddemerits with respect to such demands as noted above, and fail torespond to the demands of the current industrial world. The presentinvention is a new invention in connection with these various matters.The aforementioned problems with respect to the prior arts will bebriefly mentioned in order to better understand the background of thepresent invention.

[0014] Article 1: The number of parts and the number of assembly stepsso increase as not to make a good use of the plastic package, i.e., thelow cost. That is why the metallized package and the plastic package arejointly used.

[0015] Article 2: The cylindrical receptacle is formed in a part of theresin case. Considering the dimensional accuracy of the receptacleitself and the deformation of the receptacle caused by the insert- andpull force of connector and the thermal expansion, the module in Article2 can be applied to a light emitting diode having a large spot size butis not suitable for a laser diode having a small spot size.

[0016] Article 3: A light source for an optical disk is concerned, whichis not used for transmission of an optical fiber as in the presentinvention. Naturally, consideration of the seal of fiber and thereliance of optical coupling is not taken in Article 3.

[0017] Article 4: Only the bare portion of the pigtail fiber is sealedwith resin, and the jacket portion is exposed to outside. Accordingly,the thermal stress and the external force are concentrated on theinterface between the bare fiber portion and the jacket portion to bringforth a problem in that the bare fiber is broken. There is a difficultythat since when the casting is performed, voids tend to be mixed, watermoves in from the channel to corrode optical ends of optical devices andelectrodes.

[0018] Article 5: While the pigtail fiber is received in the hollowresin case, reference is not made to the thermal stress and moistureresistance of the resin case. Further, reference is not made tomaterials for the resin case and molding method. In this technique,various problems occurs unless various items mentioned above aresufficiently selected. That is, due to a difference in the coefficientof thermal expansion between the bare fiber (quartz glass) and the resincase, the bare fiber protrudes from the jacket, and the crack occurs inthe bare fiber due to the concentration of stress. Further, vaporpermeated into the hollow case becomes dewed on the surface of theoptical device or the bare fiber to give rise to the corrosion of theoptical device, or to progress the growth of crack, resulting in therupture of the bare fiber.

[0019] Article 6: The optical device and the ferrule with fiber aresandwiched between the silicon substrate and the silicone cap, andsealed. However, the elastic modulus of the resin package member and theanisotropy of the thermal coefficient of expansion of the resin packagemember are not taken into consideration.

[0020] As briefly mentioned above, the prior arts lack someconsideration in relation to the number of parts, thermal stress andmoisture resistance concerned with the cost. The present inventionprovides an optical module compatible with the lower cost and the higherreliance by the plastic packaging technique.

DISCLOSURE OF INVENTION

[0021] A first object of the present invention is to secure thereliability of an optical module while reducing the molding cost of aresin case type package.

[0022] A second object of the present invention is to secure thelong-term stability of an optical coupling between an optical elementand an optical fiber while reducing the molding cost of a resin casetype package. That is, it is to provide a means which suppressesdeformation of the resin case caused by the change in temperature andthe external force to reduce stress applied to constituent members ofthe optical module.

[0023] A third object of the present invention is to provide a means forfurther enhancing the moisture resistance of constituent members of anoptical module such as an optical device and an optical fiber whilereducing the molding cost of a resin case type package. Thereby, thelong-term stability of the optical module is to be secured. By the jointuse with the means for securing the long-term stability of the opticalcoupling between the optical device and the optical fiber mentioned inthe above second object, it is possible to secure more sufficient andlong-term stability of the optical module.

[0024] A fourth object of the present invention is to secure thereliability of an optical module while reducing the molding cost of acomprehensive molding type package.

[0025] A fifth object of the present invention is to secure thelong-term stability of an optical coupling between an optical device andan optical fiber while reducing the molding cost of a comprehensivemolding type package. That is, it is to provide a means which suppressesdeformation of the resin case caused by the change in temperature andthe external force to reduce stress applied to constituent members ofthe optical module.

[0026] A sixth object of the present invention is to provide a means forfurther enhancing the moisture resistance of constituent members of anoptical module such as an optical device and an optical fiber whilereducing the molding cost of a comprehensive molding type package.Thereby, the long-term stability of the optical module is to be secured.By the joint use with the means for securing the long-term stability ofthe optical coupling between the optical device and the optical fibermentioned in the above fifth object, it is possible to secure moresufficient and long-term stability of the optical module.

[0027] A seventh object of the present invention is to provide a meansfor constituting the optimal electric connection to an optical devicewhile securing the reliability of an optical module and the reduction ofthe molding cost of a resin case type package.

[0028] An eighth object of the present invention is to provide a meansfor constituting the optimal electric connection to an optical devicewhile securing the reliability of an optical module and the reduction ofthe molding cost of a comprehensive molding type package.

[0029] A ninth object of the present invention is to provide an opticalcommunication apparatus having an optical module of low cost and highreliability mounted thereon, and an optical communication system.

[0030] Various inventions disclosed in the present specificationparticularly relate to the following two aspects in solving theaforementioned problems. The first is an aspect of a resin packagemolding method. The second is an aspect of a method for mounting anoptical device and an optical fiber into the resin package. In thepresent specification, the resin package molding method is dividedroughly, and the individual molding methods will be explained in detail.

[0031] The resin package molding method is divided roughly into twokinds. First, a method of using a resin case premolded (hereinafterreferred to as a resin case type) is used. Secondly, a method forcomprehensively insert-molding an optical device with other variousconstituent parts (hereinafter referred to as a comprehensive moldingtype method) is used. In the case of the above-described resin casetype, an injection method is suitable for molding a resin case. On theother hand, in the comprehensive molding method, a transfer molding issuitable.

[0032] It is noted that the optical devices in the present specificationinclude active optical devices such as a semiconductor laser device, anoptical amplifier, an optical modulator, an optical switch, etc.,passive optical elements such as a semiconductor light receiving device,an optical coupler, an optical wavelength multiplexer/demultiplexer,etc., a hybrid optical integrated circuit in which optical elements aremounted on an optical waveguide base plate or an electronic circuit baseplate, a monolithic integrated optical circuit having optical elementsand an electronic circuit integrated, and an optical element as fiber.Further, as the aforementioned various optical devices, a semiconductordevice having an active region mainly formed of a semiconductormaterial, and a dielectric optical device having an active region formedof a dielectric material can be also used.

[0033] As optical fibers, there can be used, in addition to a singlemode quartz fiber, a multimode fiber, a plastic fiber, and so on. Notonly one but a plurality of optical fibers can be used. Forms of fibersinclude a form used as a fiber array and a fiber ribbon, and a form forremoving or connecting fibers on some surfaces of the package.

[0034] In the following, with respect to the details of the presentinvention, a method of a resin case type will be first explained, and acomprehensive molding method will then be explained.

[0035] <Resin case type molding method>

[0036] Main forms of the present invention belonging to the resin casetype are as listed below. It is noted that the contents of detailedexplanation thereof, further improved inventions, and modifiedinventions will be also explained.

[0037] A first mode of the optical module according to the presentinvention has the following constitution. That is, there comprises anoptical device, an optical fiber optically coupled to the opticaldevice, and a resin case member for mounting at least the optical deviceand the optical fiber thereon, the direction along an optical axis ofthe optical fiber; being the direction of the high elastic modulus of aresin material of a main portion along the optical axis of the opticalfiber of the resin case member.

[0038] Since the direction of the optical fiber is the direction of thehigh elastic modulus in the resin having the anisotropy in the elasticmodulus particularly at the main portion along at least the optical axisof the optical fiber in the base of the resin case member, thedeformation of the resin case due to the mechanical external force andthe difference in the thermal expansion is suppressed. The resin casemember is inexpensive as compared with the ceramic package, and theresin case is free from deformation whereby the manufacturing yield canbe enhanced, and the manufacturing cost price can be reduced.

[0039] A second mode of the optical module according to the presentinvention comprises an optical device, an optical fiber opticallycoupled to the optical device, and a resin case member for mounting atleast the optical device and the optical fiber thereon, the directionalong an optical axis of the optical fiber being the direction of thelow coefficient of thermal expansion in a resin material of a mainportion at least along the optical axis of the optical fiber in theresin case member.

[0040] Since the direction along an optical axis of the optical fiber isthe direction of the low coefficient of thermal expansion in a resinmaterial at a main portion along the optical axis of the optical fiberin the resin case member, the deformation of the base due to the heat issmall, and the misalignment for coupling between the optical device andthe optical fiber does not occur. It is noted that the generation sourceof heat for occurrence of such a phenomenon as described in question isfor example, a change in temperature of external environment or heatgeneration of the optical device itself in the package.

[0041] The resin case member is inexpensive as compared with the ceramicpackage, and the resin case is free from deformation whereby themanufacturing yield can be enhanced, and the manufacturing cost pricecan be reduced.

[0042] A third mode of the optical module according to the presentinvention comprises an optical device, an optical fiber opticallycoupled to the optical device, and a resin case member for mounting atleast the optical device and the optical fiber thereon, the orientationof a molecular chain of the resin being substantially parallel with theoptical axis of the optical fiber in a main portion along an opticalaxis of the optical fiber in the resin case member.

[0043] Since the orientation of a molecular chain of the resin of themain portion along the optical axis of the optical fiber beingsubstantially parallel with the optical axis of the optical fiber, it ispossible to enhance the elastic modulus of the case in the direction oforientation of the molecular chain and to reduce the coefficient ofthermal expansion as a result. Accordingly, the deformation of the basedue to the external stress or thermal stress is small, and the deviationin position between the optical device and the optical fiber does notoccur. It is noted that the generation source of heat for occurrence ofsuch a phenomenon as described in question is for example, a change intemperature of external environment or heat generation of the opticaldevice itself in the package.

[0044] The resin case member is inexpensive as compared with the ceramicpackage, and the resin case is free from deformation whereby themanufacturing yield can be enhanced, and the manufacturing cost pricecan be reduced.

[0045] A fourth form of the optical module according to the presentinvention comprises an optical device, an optical fiber opticallycoupled to the optical device, and a resin case member for mounting atleast the optical device and the optical fiber thereon and having a mainflowing direction of the resin substantially parallel with the opticalaxis of the optical fiber.

[0046] According to the above-described molding method, the direction ofthe optical axis of the optical fiber is generally parallel with theorientation of the molecular chain of the resin constituting thelengthwise direction of the resin case. Therefore, it is possible toenhance the elastic modulus of the case in the direction of orientationof the molecular chain and to reduce the thermal expansion rate as aresult.

[0047] Preferably, in molding the resin case as described, there isprovided a gate for injecting the resin at a fiber supporting portion, apart in the vicinity thereof, or a part opposite to the supportingportion to inject the resin into a mold. By injecting the resin from theaforementioned part, it is possible to make the direction of the opticalaxis of the optical fiber and the orientation of the molecular chain ofthe resin constituting the lengthwise direction of the resin casegenerally parallel. This molding method is suitable to be used for (1)the pigtail type optical module and (2) the receptacle type opticalmodule.

[0048] The resin case member according to the aforementioned moldingmethod is inexpensive as compared with the ceramic package, and theresin case is free from deformation whereby the manufacturing yield canbe enhanced, and the manufacturing cost price can be reduced.

[0049] In this case, more practically, it is preferable that a leadframe is premolded integrally with a resin package member. That is, whenthe resin is caused to flow substantially parallely with the opticalaxis of the optical fiber to mold the resin package member, the leadframe is inserted in advance at a predetermined position, and athermoplastic resin is caused to flow for injection molding.

[0050] According to this means, since the resin case and the lead frameas an electric terminal can be integrated and supplied, the handling inassembly of the module is simple. Further, since the optical device andthe optical fiber can be firmly located to the substrate, opticalcoupling can be stabilized without disturbing alignment between theoptical device and the fiber by the distortion of the case caused by theexternal force or the change in temperature. Furthermore, heat generatedby the optical device is released through the lead frame.

[0051] In the case where the optical module is produced using the resincase type, it is important, from a viewpoint of an idea of the methodfor molding the resin package, when the resin case is injection-molded,to place the optical fiber in the resin case so that the flowingdirection of the thermoplastic resin within the mold is generallyparallel with the direction of the optical axis of the optical fiber.When various members are sealed in the case, it is possible to suppressthe deformation of the case caused by the external force or the changein temperature, and suppress the deformation of the case caused by thechange in temperature or the external pressure. Because of this, it ispossible to prevent an occurrence of deterioration in optical couplingcharacteristics caused by the positional deviation between the opticaldevice and the fiber, and cracks in the fiber surface, as a consequenceof which the reliability of the optical module can be enhanced. Theoptical coupling between the optical device and the fiber can bemaintained stable for a long period of time.

[0052] There are two kinds of case materials for the resin case type,which are a thermosetting resin and a thermoplastic resin. A typicalexample of the thermosetting resin that can be mentioned is an epoxyresin. Examples of the thermoplastic resins that can be mentionedinclude a liquid crystal polymer (LCP) of a glass fiber-reinforcedgrade, a cross-linked type polyphenylene sulfide (PPS) resin, a linearPPS resin, a polybutylene terephthalate (PBT) resin and so on of afiller-reinforced grade and a carbon fiber-reinforced grade.

[0053] As the resin used for the resin case method, the thermoplasticresin is particularly preferable. Because the thermoplastic resin hasthe advantages as follows: (1) The molding cycle time is short ascompared with the thermosetting resin. (2) The resin loss ratio is low.(3) Recycle materials can be used. That is, together with the merit ofthe above (1), since the using quantity of resins can be reduced, it isuseful for reducing the cost. (4) Burr is small due to the low pressureinjection molding. (5) The cure after molding is unnecessary. On thebasis of these advantages, it is possible to produce the resin case atlower cost. It is noted that the fact that a molding temperature isrelatively high poses little problem in production of the resin case.

[0054] Further, it is possible to easily arrange the orientation of themolecular chain by carrying out the injection molding with the resinmentioned above. Particularly, it is possible to more easily arrange theorientation of the molecular chain with a linear PPS or a liquid crystalpolymer. Accordingly, it is possible to realize lower stress by placingthe fiber within the case along the aforementioned orientation toachieve the higher reliability as a result. Since the thermoplasticresin allows the molecular chain to be oriented in the flowing directionof resin when molding as described above, it is important to take intomechanical and thermal anisotropy. Deformation tends to occur relativeto external force, or time passage positional deviation (creep) betweenthe optical device and the fiber or crack in fiber due to the thermalstress sometimes is induced unless the dependency of elastic modulus orcoefficiency of thermal expansion is taken into consideration.

[0055] It is noted that the thermosetting resin can be also used for thepresent method of resin case type. However, the use of the thermoplasticresin is advantageous in terms of price as compared with the use of thethermosetting resin.

[0056] Next, the sealing of the optical device and the optical fiberwithin the resin package in the case of the resin case type will beexplained.

[0057] In the case of the resin case type, the procedure itself of themanufacturing method may employ the usual procedure. At least theoptical device and the optical fiber are placed on the base of the resinpackage, and the package is completed using the cap. More practically,the substrate having the optical device and the optical fiber securedthereto is placed on the resin case in which the lead frame is insertedexcept the outer lead portion and subjected to injection molding.

[0058] In the resin case type, the sealing method for the optical deviceand the optical fiber within the package can be mainly classified intothree kinds. A first method comprises a method for filling a transparentresin into a resin case by a potting injection method, a second methodcomprises a method for mounting a cap on a resin case to seal theinterior of the case leaving to be hollow, and a third method comprisesa method for sealing a resin case and a cap after a transparent resinhas been dropped onto an optical device and a fiber. Of these methods,the first method, i.e., the potting injection method is more preferable.

[0059] The second method has a problem of the dewing to the opticaldevice and the fiber, and the deterioration of the optical device andthe rupture of the fiber resulting therefrom. As compared with the firstand third methods, the first method, i.e., the potting injection methodin which the case is internally filled with resin is more preferable inorder to suppress the deformation of the resin case and the stress ofthe fiber as less as possible. In this case, the optical device and theoptical fiber are coated directly with the transparent resin.

[0060] According to this means, the optical device and the optical fiberare coated directly with the transparent resin whereby water moved intothe resin case (which cannot be avoided under the high temperature andhigh humidity environment for a long period of time) can be preventedfrom moistening to the optical surface of the optical device and thesurfaces of the electrode and the fiber.

[0061] Further, the joint use of the sealing method for the opticaldevice and the optical fiber within the package and the molding methodfor various resin package members according to the present inventionscan obtain the following effects. That is, together with the effect ofthe lower stress based on the molding method for the resin packagemember, the adhesion of the transparent resin to the optical device andthe optical fiber can be secured. The stress of the optical deviceitself is relieved because the resin case has the high elasticity andlower thermal expansion, and the adhesion of the transparent resin tothe optical element and the optical fiber and the transparent resin canbe secured. Accordingly, there is the effect that the corrosion of theoptical device and the crack of the fiber caused by formation of a waterfilm can be prevented, and the moisture resistance can be enhanced.

[0062] Further, the change in temperature of the external environment isrelieved within the resin case. Furthermore, the enhancement of theenvironment resistance by the transparent resin used to seal the opticalfiber is remarkable.

[0063] The transparent resins for directly coating the optical deviceand the fiber that can be used include thermosetting resins, forexample, such as a silicone gel of a silicone resin, silicone rubber, alow stress epoxy resin, an acrylic resin, a urethane resin, etc.

[0064] It is noted that the laser diode for the optical disk mentionedin Article 3 in the column of the prior art is coated directly with thesilicone resin as measures for optical damage. However, since the laserdiode for fiber optic transmission has long in oscillation wavelengthand emits relatively smaller optical output, the optical damage causedby absorption of light and thermal decomposition as in the optical diskis hard to occur. Accordingly, in the optical transmission system, it isless necessary to expect for the packaging resin the role as measuresfor optical damage as in Article 3. Article 3 is different from thepresent invention in a viewpoint of such a selection.

[0065] <Comprehensive molding method>

[0066] In the following, the comprehensive molding method will beexplained.

[0067] The optical module in the fifth mode of the present inventionaccording to the comprehensive molding method has the followingconstitution. That is, when the optical device and the optical fiber areinserted for transfer molding, the thermosetting resin is flown so as tobe generally parallel with the direction of the optical axis of theoptical fiber within the mold for molding. This method can reduce theflew resistance of the resin applied the fiber, and reduce thepositional deviation and the residual distortion of the fiber.Accordingly, it is possible to prevent the deterioration of the opticalcoupling characteristic caused by the positional deviation between theoptical device and the fiber and the occurrence of the crack in thefiber surface, thus enabling enhancement of the reliability of theoptical module as a result.

[0068] Further, the present means has the effect that the optical deviceand the optical fiber can be molded stably and comprehensively in ashort period of time by the transfer molding, and the cost can bereduced. Further, the molten thermosetting resin is flown along thefiber placed within the mold whereby fluctuation of the optical couplingcharacteristic during molding can be suppressed (for example, the lowviscosity resin and the low speed molding are further effective), andthe residual stress applied to the fiber after molding can be reduced.For example, the low elastic resin and the low thermal expansion resinare further effective. With this, the reliability of the optical moduleincluding the moisture resistance can be enhanced.

[0069] It is noted that when in molding, for example, the use of the lowviscosity resin and the low speed molding are further effective in orderto display the effects of the present invention. For solving the problemafter molding, the use of, for example, the low elastic resin and thelow thermal expansion resin is further effective.

[0070] As the resin used for the comprehensive molding method, thethermosetting resin is preferable. The typical examples of the baseresin that can be listed include an epoxy resin and a silicone resin. Ofcourse, a filler and a elasticizer as desired can be added similar tothe case of the practical use of the usual thermosetting resin.

[0071] The comprehensive molding generally includes two methods, whichare a casting injection method and a transfer molding method. For theformer, mainly a liquid epoxy resin is used, and for the latter, mainlya tablet is used in which a powdery epoxy resin is pressed.

[0072] The transfer molding method is suitable for the lower cost andmass production. Because the transfer molding method has the followingadvantages as compared with the casting injection method. That is, (1)the molding time is short, (2) the vacuum defoaming process isunnecessary, and (3) the shape dimension and reliability are stable.

[0073] However, in the transfer molding in the case where there are nometallized package and cap, the transfer pressure of resin is applied tothe optical device and the fiber, resulting in the positional deviationbetween the optical device and the fiber, and the distortion of thefiber and the optical device-mounted base plate. Accordingly, it isnecessary to take the flowing direction of resin during molding intoconsideration. This positional deviation deteriorates the couplingcharacteristic of the optical device and the fiber. Further, since thedistortion acts as the internal residual stress, this influences on thelong-term reliability of the optical module.

[0074] It is noted that even in the resin case type, the orientation ofthe molecular chain by the flowing direction comprises a main point, andit is understood that the flowing direction is important for both theresin case type and the comprehensive molding type.

[0075] In this case, in the case of the transfer molding, it is suitablethat the lead frame is inserted in advance into a predeterminedposition, and the thermosetting resin is flown generally parallel withthe optical axis of the optical fiber to effect the transfer molding.

[0076] According to this means, the optical device and the optical fibercan be stable held on the base plate, and in addition, the base plate isfixed upwardly or downwardly of the lead frame and the transfer moldingis performed to enable electric connection simply.

[0077] The sealing method for the optical device and the fiber in thecomprehensive molding type can be mainly classified into four methods asfollows: A first method is a method for directly molding an opticaldevice or an optical fiber with a transparent resin, a second method isa method for molding an optical device or a fiber with an opaque resin(colored, mainly black) after being sealed with a cap, a third method isa method for molding them using a transparent resin after dropping atransparent resin on them, and a fourth method is a method for furthermolding them using a opaque resin after dropping it.

[0078] Since a cap is preferably omitted in order to reduce the numberof parts to lower the cost, it is necessary for the resin for directlycoating the optical device to be transparent. In order to prevent thestray light which comes in and goes out of the module, it's outermostsurface is preferably opaque. Accordingly, the fourth method which hasnot been present in the past is more desirable, which molds an opaqueresin on a dropped transparent resin.

[0079] In the case of the comprehensive molding method, the followingstep is taken. At least the optical device and the optical fiber areplaced on the base of the package, and the transparent resin is droppedon the optical device and the fiber to fix them. By doing so, theoptical device and the fiber are directly encapssulated with thetransparent resin, after which the transfer molding is performed.

[0080] More practically, at least the optical device, the fiber, and thelead frame are fixed to the substrate, and the base plate assembly isinserted to the module, and the transfer molding is performed except theouter portion of the fiber and the outer lead portion of the lead frame.

[0081] According to the means for directly coating the optical deviceand the optical fiber with the transparent resin, the deterioration ofthe optical device or the fiber caused by the moisture absorption of thetransfer molding package can be prevented, and in addition, the moldingpressure applied to the coupling portion between the optical device andthe optical fiber can be dispersed, and the residual stress aftermolding can be relieved. Accordingly, there is the effect that theoptical coupling characteristic between the optical device and theoptical fiber can be further stabilized, and the reliability of theoptical module can be further enhanced.

[0082] In the module for fiber optic transmission, the silicone resin isnot necessary for preventing optical damage. However, silicone isadvantageous in the following point. Paying attention to the fact thatthe elastic modulus of the silicone resin is lower than that of theepoxy resin, the thermal stress applied to the optical device or thefiber is relieved so that the interface between the optical device andthe resin is prevented from peeling. Accordingly, the corrosion causedby formation of a water film at the interface can be prevented.

[0083] It is noted that in the case where the transfer molding isemployed in the comprehensive molding type, since the transfer pressureis applied to the transparent resin, the elastic modulus of thetransparent resin should be high to some extent in order to preventdeformation. That is, it is necessary to select a transparent resinhaving the elastic modulus compatible with the lower thermal stress andthe deformation prevention.

[0084] Various optical modules described above are mounted on the wiringsubstrate of the optical communication apparatus to make the opticalcommunication apparatus high reliability and realize it at less cost. Inthis way, it is possible to provide an optical communication systemwhich has high reliability and is inexpensive.

[0085] The effects of the present invention can be arranged as follows:

[0086] According to the first mode of the present invention, since thedirection of the optical axis of the optical fiber of the resin casemember is the direction of high elastic modulus in the resin,particularly at the main portion along at least the optical axis of theoptical fiber in the base, the deformation of the base caused by theexternal heat is small, and the positional deviation between the opticaldevice and the optical fiber does not occur.

[0087] According to the second form of the present invention, since thedirection along an optical axis of the optical fiber is the direction ofthe low coefficient of thermal expansion in a resin material at a mainportion along the optical axis of the optical fiber in the resin casemember, the deformation of the base caused by the external heat issmall, and the positional deviation between the optical device and theoptical fiber does not occur.

[0088] According to the third mode of the present invention, since atthe main portion supporting at least the optical axis of the opticalfiber in the resin case, the orientation of the molecular chain of theresin is substantially parallel with the optical axis of the opticalfiber, the elastic modulus of the case in the direction of orientationof the molecular chain is enhanced, and as a result the thermalexpansion rate can be reduced. Accordingly, the deformation of the basecaused by the external heat is small, and the positional deviationbetween the optical device and the optical fiber does not occur.

[0089] According to the fourth mode of the present invention, thedirection of the optical axis of the optical fiber is generally parallelwith the orientation of the molecular chain of the resin constitutingthe lengthwise direction of the resin case. Because of this, the elasticmodulus of the case in the direction of the orientation of the molecularchain is enhanced, and as a result, the thermal expansion are can bereduced. Accordingly, the deformation of the case caused by the changein temperature and the external force can be suppressed, and the stressapplied to the constituent member of the optical module is reduced. As aresult, the optical coupling between the optical device and the fibercan be maintained stable for a long period of time.

[0090] According to the fifth form of the present invention, it ispossible to comprehensively mold the optical device and the fiber by thetransfer molding stably and in a short period of time, the lower costcan be achieved, the molten thermosetting resin is flown along the fiberinstalled within the mold to enable the suppression of variation of theoptical coupling characteristic during molding, and the residual stressapplied to the fiber after molding can be relieved. Accordingly, thereliability of the optical module including the moisture resistance canbe enhanced.

[0091] The present invention is capable of providing an opticalcommunication apparatus and an optical communication system which arelow in price and has a high reliability.

BRIEF DESCRIPTION OF DRAWINGS

[0092]FIG. 1A is a plan view of assistance in explaining the pigtailtype optical module according to a first embodiment of the presentinvention.

[0093]FIG. 1B is a sectional view in the direction parallel to theoptical axis of assistance in explaining the pigtail type optical moduleaccording to the first embodiment of the present invention.

[0094]FIG. 1C is a sectional view in the direction crossing with theoptical axis of assistance in explaining the pigtail type optical moduleaccording to the first embodiment of the present invention.

[0095]FIG. 2A is a plan view of assistance in explaining the pigtailtype optical module according to a second embodiment of the presentinvention.

[0096]FIG. 2B is a sectional view in the direction parallel to theoptical axis of assistance in explaining the pigtail type optical moduleaccording to the second embodiment of the present invention.

[0097]FIG. 2C is a plan view showing the mode for manufacturing thepigtail type optical module according to a second embodiment of thepresent invention.

[0098]FIG. 3A is a plan view of assistance in explaining the receptacletype optical module according to a third embodiment of the presentinvention.

[0099]FIG. 3B is a sectional view in the direction parallel to theoptical axis of assistance in explaining the receptacle type opticalmodule according to the third embodiment of the present invention.

[0100]FIG. 4A is a plan view of assistance in explaining the receptacletype optical module according to a fourth embodiment of the presentinvention.

[0101]FIG. 4B is a sectional view in the direction parallel to theoptical axis of assistance in explaining the receptacle type opticalmodule according to the fourth embodiment of the present invention.

[0102]FIG. 5 is a perspective view of assistance in explaining the cardtype optical module according to a fifth embodiment of the presentinvention.

[0103]FIG. 6 is a view of assistance in explaining the opticalcommunication system according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION EMBODIMENT 1

[0104] The first embodiment is an example of the aforementioned “resincase type”, more concretely, an example of a pigtail type opticaltransmission module for a resin case type package. The maincharacteristic thereof lies in that when a base and a cap of the packageare molded, the flowing direction of a liquid crystal polymer isparallel with the direction of an optical axis of the optical fiber.With this, a molecular chain is oriented along the direction of theoptical axis. Thereby, the elastic modulus of the optical package andthe cap in that direction can be improved, and the coefficient ofthermal expansion can be reduced. It is noted in this example that as apackage molding method, an injection molding method is employed, and asa sealing method for an optical element and an optical fiber, a droppingmethod is employed. For the dropping, a low elastic resin is used.

[0105] The first embodiment according to the present invention will beexplained in detail with reference to the drawings. FIGS. 1A, 1B and 1Care respectively views of assistance in explaining the optical moduleaccording to the first embodiment of the present invention. Thesedrawings show the pigtail type optical transmission module for the resincase type package. FIG. 1A is a partial plan view as viewed from thetop, FIG. 1B is a partial sectional view as viewed from the side, andFIG. 1C is a sectional view in the direction crossing with the opticalaxis of the optical fiber.

[0106] As shown in FIGS. 1A, 1B and 1C, the resin case type plasticpackage receives therein optical devices 10, 11, a bare fiber 20 at theextreme end of the pigtail type optical fiber, and a substrate 30 formounting members such as the optical devices. These members are sealedwithin a cavity 44. The cavity 44 is formed mainly by a base 40 and acap 80. A lead frame 50 is formed integrally with a resin case typeplastic package 40.

[0107] The optical devices 10, 11 are provided on the substrate 30 bydie-bonding, and the bare fiber 20 is fixedly mounted in a V groove 31provided in the substrate 30. In this manner, the optical device 10 andthe fiber 20, and the optical device 10 and the optical device 11 areoptically coupled with each other. The extreme ends of the opticaldevices 10, 11 and the fiber 20 are encapsulated with a transparentresin 60. In this manner, the substrate 30 having the optical devices10, 11 and the fiber 20 placed thereon is fixedly mounted on a die pad51 extending from the lead frame 50. The die pad 51 is installed withinthe cavity 44.

[0108] The base 40 of the plastic package is provided at one end thereofwith an optical fiber holder portion 41 normally in the form of a Ugroove. The bare fiber 20 and a jacket 21 covering the bare fiber 20 arefixedly mounted in a U groove 42 and a U groove 43, respectively. Thecap 80 is fitted over and adhered to a projection portion 45 of theplastic package 40.

[0109] The optical device 10 comprises an end-face emitting type laserdiode formed from an InP semiconductor. The emission wavelength thereofis 1.3 μm, the forward output is for example, 7 mW, and the half-valuetotal angle of a far field pattern is for example, 25×30° (approximately1.1×0.9 μm in spot size).

[0110] The optical device 11 comprises an end-face receiving type (awaveguide type) photodiode formed from an InP semiconductor, in order tomonitor a rearward output of the optical device 10. The optical devices10, 11 are provided at a predetermined position of the substrate 30 bydie-coupling by means of an Au—Sn solder in junction down manner. Amarker for alignment relative to the substrate 30 is formed on thesurface on the junction side of the optical devices 10, 11. It is set sothat the thickness of the Au—Sn solder layer is for example, 3 μm, andthe height of an active layer of the optical devices 10, 11 from thesurface of the substrate 30 is for example, 8 μm.

[0111] The optical fiber 20 comprises a single mode quartz fiber. Theoutside diameter is for example, 125 μm, and the spot size is forexample, 5 μm. The emission light of the optical device 10 is coupled tothe fiber 20, propagated within the optical fiber 20 in the optical axisdirection 23 and output. In the case where the end of the optical fiber20 is vertically cut and coupled to the optical device 10 by thebutt-joint coupling system, the coupling efficiency of approximately −8dB on the maximum is obtained. In the case where a lens is formed on theend of the optical fiber 20 by etching by way of a buffer fluorinesolution or by a discharge melting processing and coupled by aprespherical lens-end coupling system, approximately 3 dB on the maximumis obtained. The rear portion of the optical fiber 20 is protected bymeans of a jacket 21 to constitute a pigtail fiber. The jacket 21 isformed of nylon and has the outside diameter of, for example, 0.9 mm.The portion adhered to the U groove 43 of the jacket 21 is sometimesapplied with a roughening processing or chemical processing in order toimprove the adhesive properties.

[0112] The base plate 30 is formed from, for example, a silicon crystalsubstrate of a surface orientation (100). The substrate 30 is providedwith a V groove 31 for locating the optical fiber 20 with high accuracy,and a wiring 33 for driving the optical devices 10, 11. A marker foralignment (not shown) is formed at a position for fixing the opticaldevices 10, 11. The V groove 31 and the marker are constituted using the(111) crystal surface of the silicon crystal and the surface equivalentthereto.

[0113] The V groove is simultaneously formed by anisotropic etchingrelative to the silicon crystal surface in a KOH aqueous solution. The Vgroove 31 has the width of, for example, 142 μm, and is processed sothat the height of the optical axis at the extreme end of the fiber 20coincides with the height of the active layer of the optical devices 10,11 as viewed from the surface of the substrate 30.

[0114] The wiring 33 comprises a normal Au/Pt/Ti film or Au/Ni/Cr filmand is vapor-deposited on the insulating film of the surface of thesubstrate 30. While a wiring pattern in FIG. 1A-1 is depictedschematically, it is to be noted of course that the width and thicknessof the wiring 33, and the thickness of the insulating film aredetermined in consideration of the load capacitance and the thermalresistance of the optical devices 10, 11.

[0115] The package base 40 comprises a dual inline package (DIP) of8-pin. An external form of the package 40 in the present embodiment isillustrated such that the length is 14.6 mm (including the length (5 mm)of the fiber holder portion), the width is 6.3 mm, and the height is 3mm. The package base 40 is provided with a cavity 44, U grooves 42, 43,and a projection 45. The widths of the U grooves 42, 43 correspond tothe outside diameter of the fiber 20 and the jacket 21 secured thereto(in consideration of FIG. 1C). In this manner, the sealability of thepackage 40 is improved, and the protrusion of the fiber 20 from thejacket 21 is prevented. The depth of the U grooves 42, 43 is designed sothat the height of the fiber 20 increases from the extreme end thereof(V groove 31) to the U groove 42. This is because the distortion causedby the external force and the thermal expansion are absorbed by flexureof the fiber 20. The projection portion 45 in the outer periphery of thepackage 40 is provided in order to increase the rigidity of the base 40of the package and to improve the adhesive properties thereof with thecap 80.

[0116] The base 40 and the cap 80 of the package are formed of a blackliquid crystal polymer which is one kind of thermoplastic resins. Theyare subjected to injection molding by flowing, in molding, the liquidcrystal polymer in the directions indicated by arrows 47, 87 from gateportions 46, 81. In the mold in the first embodiment, pin gates areused, and the gate portions 46, 81 are positioned on the upper and lowersurfaces of the fiber holder portion 41. The flowing directions 47, 87of the resin are substantially parallel with the optical axis direction23 of the fiber 20. For the mold itself, a normal mold will suffice. InFIG. 1B, the mold is not shown.

[0117] The liquid crystal polymer has a variety of grades. In the firstembodiment, a glass-fiber reinforced grade was selected from a viewpointof high rigidity, low thermal expansion and moldability. In molding ofthe liquid crystal polymer, since the molecular chain is orientedstrongly in the flowing direction, attention was also paid to theanisotropy in the direction at right angles (⊥) with the flowingdirection (//). In the liquid crystal polymer used in the firstembodiment, the elastic modulus is 14 GPa (//) and 4 GPa (⊥), thecoefficient of thermal expansion is 5 ppm/° C. (//) and 60 ppm/° C. (⊥),and the shrinkage ration in molding is 0.1% (//) and 0.5% (⊥). As othertypical characteristics, the dielectric constant is approximately 4, thewater absorption rate is 0.01%, and the soldering heat resistance is 30seconds at 300° C. With respect to the moldability, good molding lessburr can be carried out under the conditions of 350° C. of cylindertemperature, 80° C. of mold temperature, 40 MPa of injection pressure,and 20 seconds of molding cycle time.

[0118] The lead frame 50 is insert-molded into the base 40 of thepackage. As materials for the lead frame 50, in the case where theoptical device 10 is used at high output/high temperature, and in thecase where it is used at relatively low output/low temperature, a Cualloy of high heat conductivity, and a Fe—Ni alloy of low heatexpandability are respectively used. A die pad 51 and inner leads 52-1to 8 to which the substrate 30 is fixed secured are exposed to the innersurface of the cavity 44, and outer leads 53-1 to 8 extend externally ofthe package 40. The pitch of the outer leads 53-1 to 8 is for example,2.54 mm, and the width between the 53-1 to 4 and 53-5 to 8 is forexample, 300 mil (7.62 mm). The die pad 51 is connected to the outerleads 52-2 and 52-7. The outer leads 53-6, 7 are electrically connectedto the optical device 10 through Au wires 70, 71, and the outer leads53-4, 5 are electrically connected to the optical device 11.

[0119] The transparent resin 60 comprises a soft gel-like siliconeresin. The refractive index of the transparent resin 60 in thewavelength of 1.3 μm is 1.4, which generally matches with that of theoptical fiber 20. The transparent resin 60 is coated on the opticaldevices 10, 11 and the extreme ends of the optical bare fiber 20 (thewhole surface of the bare fiber 20 according to the specification ofreliability) into intimate contact therewith. Further, the transparentresin is filled between the forward end of the optical device 10 and theend of the optical fiber 20, and between the rearward end of the opticaldevice 10 and the light receiving end of the optical device 11 toenhance the optical coupling efficiency therebetween (enlarging theallowable accuracy of alignment) and eliminate the reflecting andreturning light from the end of the optical fiber 20 to the opticaldevice 10.

[0120] Next, the assembly steps of Example of the optical module 1according to the first embodiment will be explained schematically.

[0121] (1) The base 40 and the cap 80 of the package areinjection-molded in advance by a well-known method. In this case, it isimportant, as described in detail previously, that particularly, thebase 40 be molded by flowing the resin so as to be substantiallyparallel with the optical axis of the optical fiber.

[0122] (2) The markers for the optical devices 10, 11 and the substrate30 are recognized, for example, by an infrared ray image to effectalignment thereof. The load force is applied to the optical devices 10,11, which are temporarily pressed to the substrate 30 preheated.

[0123] (3) An Au—Sn solder is caused to reflow, and the optical devices10, 11 are subjected to die bonding to the substrate 30.

[0124] (4) The substrate 30 is fixedly adhered to the die pad 51 by aelectro-conductive (high heat conductive) epoxy resin.

[0125] (5) A portion between the optical devices 10, 11 and the wiring33 of the substrate 30 and a portion between the wiring 33 and the innerleads 52-4 to 7 are subjected to bonding by wires 70, 71.

[0126] (6) The extreme end of the optical fiber 20 is fixedly adhered tothe V groove 31 by a ultraviolet curable resin so that a spacing betweenthe forward end of the optical device 10 and the end of the fiber 20assumes a predetermined distance.

[0127] (7) The optical fiber 20 and the jacket 21 are fixedly secured tothe U grooves 42, 43 by the epoxy resin.

[0128] (8) The transparent resin 60 is dropped on the optical devices10, 11 and the optical fiber 20 to thermoset it.

[0129] (9) The cap 80 is fixedly secured to the package 40 by the epoxyresin (or welded by applying a supersonic wave) to seal the package 40.

[0130] (10) A dam bar (not shown) or a tie bar (not shown) of the leadframe 50 is cut to bend the outer leads 53-1 to 8 into a predeterminedshape.

[0131] In this manner, the assembly of the module is completed.

[0132] In Example of the optical module 1 according to the firstembodiment, the base 40 and the cap 80 of the resin case type packageare injection-molded by a liquid crystal polymer of thermoplastic resin.Thereby, as compared with the case where they are molded with generalthermosetting resin, the time required for resin hardening isunnecessary, as a result of which the molding cycle time can be reducedto ⅕. Further, burr removing process and curing after molding can beomitted.

[0133] Further, the use of the thermoplastic resin can reduce thequantity of materials used. The main reasons thereof are as follows: (1)The loss of the resin material during molding is small. (2) The recyclematerial can be molten again for use up to 20 to 25%. Thereby, there isan effect that the molding cost for the package 40 and the cap 80 can bereduced.

[0134] Since in the first embodiment, the flowing directions 47, 87 ofthe liquid crystal polymer when the base 40 and the cap 80 of thepackage are molded are parallel with the direction 23 of the opticalaxis of the optical fiber 20, the molecular chain of the liquid crystalpolymer is oriented along the optical axis direction 23. Thereby, it ispossible to enhance the elastic modulus of the optical package 40 andthe cap 80 in that direction, and to reduce the coefficient of thermalexpansion. Normally, in the pigtail type module, the tensile stress inthe optical axis direction or the bending stress is applied particularlyto the fiber holder portion. However, in the optical module shown in thefirst embodiment, the sufficient mechanical strength can be secured, andthe external stress applied to the optical fiber 20 can be suppressed.Further, the coefficient of thermal expansion of the package 40 and thecap 80 in the optical axis direction 23 is 5 ppm/° C. This value isclose to the silicon substrate 30 (3 ppm/° C.) as compared with theperpendicular coefficient (60 ppm/° C.) and the normal plastic (in orderof 10 ppm/° C.). Accordingly, since a difference from the optical fiber20 (0.5 ppm/° C.) formed of quartz is small, the thermal stress appliedto the optical fiber 20 can be reduced.

[0135] Further, in the first embodiment, both the external stress andthe thermal stress can be relieved by providing the flexure for theoptical fiber 20. That is, as shown in FIG. 1B, since the height of thebottom surface of the U groove 42 supporting the optical fiber 20 ishigher than that of the optical device 10, the optical fiber 20 isprovided with the flexure. This flexure absorbs expansion andcontraction caused by the external stress and the thermal stress.

[0136] Accordingly, according to the first embodiment, there are effectsthat the crack of the optical fiber 20 caused by the stressconcentration can be prevented, and the fluctuation of the opticalcoupling efficiency resulting from the positional misalignment of theextreme end of the optical fiber 20 caused by the stress (that is, thedeterioration of the optical output from the fiber 20) can besuppressed. Incidentally, the optical module 1 is subjected to thetemperature cycle test (−40° C.-+85° C., 1 hr/cycle), and as a result,the fluctuation of the optical output from the fiber 20 up to thousandsof cycles at the present time is within ±0.5 dB, the sufficient stressresistance being assured.

[0137] As measures for moisture resistance, in the first embodiment, theU grooves 42, 43 and the projection portion 45 are provided in the base40 of the package to enhance the adhesion between the base 40 and theouter periphery of the cap 80, between the U groove 42 and the fiber 20,and between the U groove 43 and the jacket 21. Thereby, the base 40 ofthe package can be sealed easily and certainly by the cap 80 to suppressan immersion of water into the cavity 44.

[0138] Further, the transparent resin 60 is dropped onto the opticaldevices 10, 11 and the bare fiber 20 to seal them whereby even if watermoves into the cavity 44, water is not condensed in the interfacetherebetween. In this manner it is possible to prevent the corrosion ofthe optical devices and the deterioration of the fiber 20.

[0139] Further, as the transparent resin 60, a silicone gel which issoft and has a low elasticity is used whereby even if there is adifference in thermal expansion between the optical devices 10, 11 andthe fiber 20 and the transparent resin 60, the stress applied to theinterface therebetween can be relieved, and therefore the adhesion ofthe transparent resin 60 can be secured over a long period of time.Accordingly, according to the first embodiment, there is an effect thatthe moisture resistance can be enhanced by adequately jointly using thecap sealing method and the dropping method. The optical module 1 issubjected to the high temperature high moisture operating test (85° C.,85%) in addition to the temperature cycle test. The fluctuation of theoptical output from the fiber 20 up to thousands of hours is within ±0.5dB, thus obtaining the sufficiently satisfactory result.

[0140] While in the first embodiment, a liquid crystal polymer of aglass fiber-reinforced grade is used as a package molding material, itis to be noted that other thermoplastic resin materials can be usedaccording to needs such as the rigidity, low thermal expansion,moldability, heat resistance, charging properties, flame proof, etc.These examples that can be mentioned on a liquid crystal polymer such asa filler reinforced-type grade and a carbon fiber reinforced-type grade,a cross-linked type PPS resin, a linear type PPS resin, a polybutyleneterephthalate (PBT) etc. Further, it is also possible to use a gradecapable of plating so that for example, as counter-measures forelectromagnetic noise, plating is applied to the inner surface of thecap.

[0141] A mold for injection molding in the first embodiment employs apin gate, and a gate portion is provided on the lower surface of thefiber holder portion. If the flowing direction of the resin is generallyparallel with the optical axis of the optical fiber, a side gate, asubmarine gate or the like can be used. Even if the gate portion isprovided opposite to the fiber holder portion (left-hand in FIG. 1A),the effect of the present invention can be substantially exhibited. Whenthe module is viewed from the top as in FIG. 1A, the gate portion may beprovided on the optical axis or the extending line therefrom.

[0142] Further, a plurality of cavities and a plurality of gates areprovided on the molding mold and a multiple lead frame is used whereby aplurality of packages can be molded at the same time. For example, ifthe plurality of cavities are arranged vertically to the optical axis toconstitute a mold, the number of obtaining packages increases to enhancethe productivity.

[0143] In the first embodiment, as the resin sealing method, the packageis sealed by the cap, and the optical device and the fiber are sealed bythe dropping method. However, the package is filled with the transparentresin by the potting injection method in order to enhance the stressresistance and the moisture resistance, as the case may be. Further, thecap or the transparent resin is omitted in consideration of the sealingcost and the reliability, as the case may be.

[0144] Further, while the cap material has been the same resin materialas the base of the package, it is noted that it can be sometimes changedto a metal cap or a ceramic cap for the convenience's sake of componentsupply or the like. While a transparent silicone gel has been used as asealing material for the optical device and the fiber, otherencapsulation materials, for example, such as silicone rubber, a lowstress epoxy resin (for example, silicone denatured epoxy), an acrylicresin, a urethane resin, etc. may be employed in consideration of theelastic modulus, moisture permeability, refractive index, adhesiveproperties, etc.

[0145] As forms of the package and the terminal, forms other than theDIP type illustrated in the first embodiment can be of course usedaccording to the conditions of the optical device, the optical fiber,and the optical module to be used. Examples may include a small outlinepackage (SOP) type, a plastic leaded chip carrier (PLCC) type, aleadless chip carrier (LCC) type, a pin grid array (PGA) type, a ballgrid array (BGA) type, etc. In the case where one optical element neednot be driven, for example, in the case of a passive optical element, aterminal need not be provided elecrically.

[0146] The optical devices has a wide range of application in thepresent invention including, in addition to the laser diode and thephotodiode shown in the first embodiment, active optical devices such asan optical amplifier, an optical modulator and an optical switch,passive optical devices such as an optical coupler and an opticalwavelength multiplexer/demultiplexer, a semiconductor optical device anda dielectric optical device, a hybrid optical integrated circuit inwhich optical devices are mounted on an optical waveguide substrate oran electronic circuit substrate, a monolithic optical integrated circuithaving an optical device and an electronic circuit integrated, and anoptical device as fiber.

[0147] The optical fibers that can be used include, in addition to asingle mode quartz fiber, a multimode fiber, a plastic fiber and so on.Not only one but a plurality of optical fibers may be used. Forms of thefiber include a form used as a fiber array and a fiber ribbon, and aform in which the fiber is attached or connected in some surfaces of thepackage.

[0148] Further, the present invention is effective not only in the casewhere the optical module has the fiber in explicitly but also in thecase where the receptacle type module has the fiber in implicity.

[0149] While in the first embodiment, a silicon substrate has been usedto enhance the alignment accuracy of the optical device and the fiberand enhance the heat dissipation of the optical device, but a printedboard, a ceramic substrate, a thin film substrate or the like may beused according to the specification of the processing accuracy, cost,heat resistance, dielectric constant and so on. The present inventioncan be applied to the case where no wiring is present in the substrateand the case where no substrate is used.

[0150] In the fiber optic transmission system, the optical module ismounted on the wiring substrate (a printed board, a ceramic thick-filmsubstrate, and a thin-film substrate) together with LSI and electronicparts and used as an optical communication apparatus. As shown in thefirst embodiment and other embodiments described later, the opticalmodule according to the present invention is excellent in the stressresistance and the moisture resistance in addition to the moldability,and needless to say, also as the optical communication apparatus, thelower cost and higher reliability can be realized.

EMBODIMENT 2

[0151] The second embodiment provides an example of the above-described“Comprehensive molding type package”, more specifically, an example of apigtail type optical transmission module by way of a comprehensivemolding type package. Its main characteristic lies in that when apackage is molded, the flowing direction of an epoxy resin is parallelwith an optical axis direction of a fiber. Accordingly, sincethe-flowing pressure of resin is not applied at vertically to the sideof the fiber or jacket, the fiber or the jacket is not distorted atsideways, and molding is not made in the state where the alignment ofthe optical device and the fiber is deviated. Note that in this example,as the sealing method for the optical device and the fiber, a droppingmethod using a low elastic resin is used.

[0152]FIGS. 2A and 2B are respectively views of assistance in explainingthe optical module according to the second embodiment. The presentexample shows a pigtail type optical transmission module by way of acomprehensive molding type package. FIG. 2A is a partial plan view asviewed from the top, and FIG. 2B is a partial sectional view as viewedfrom the side. FIG. 2C is a plan view showing the form in the case wherethe present modules are produced in mass using a multiple lead frame.

[0153] An optical module 100 shown in FIGS. 2A to 2C comprises opticaldevices 110, 111, an optical fiber 120, a substrate 130, acomprehensively molded plastic package 140, and a lead frame 150. Theextreme end of the pigtail fiber of the optical fiber inserted andsealed in the resin.

[0154] The optical devices 110, 111 are subjected to die bonding to thesubstrate 130. The bare fiber 120 and the extreme end of a jacket 121for coating thereof are fixedly secured to a V groove 131 and a recessedgroove 132 provided in the substrate 130 respectively. The opticaldevice 110 and the optical fiber 120, and the optical device 110 and theoptical device 111 are optically coupled each other. The base plate 130having the optical devices 110, 111 and the optical fiber 120 placedthereon are fixedly secured onto a die pad 151 extending from a leadframe 150. The jacket 121 is inserted into a fiber holder portion 141.The optical devices 110, 111 and the bare fiber 120 are encapsulatedwith a transparent resin 160.

[0155] Parts substantially similar to those shown in the firstembodiment are used for the optical devices 110, 111, the fiber 120, thesubstrate 130 and the lead frame 150. However, for the optical device110, a high power laser diode (forward output; 10 mW) was used. Theoptical devices 110, 120 are subjected to die bonding to the substrate130 by the method similar to the first embodiment. A laser beam emittedout from the optical device 110 is output along the optical axisdirection 123. The jacket 121 of the optical fiber 120 is formed of anylon resin having a higher heat resistance than the first embodimentfor carrying out transfer molding.

[0156] The substrate 130 is formed with a V groove 131 similar to the Vgroove 31, and a wiring 133 similar to the wiring 33. However, therecessed groove 132 is not present in the first embodiment. The recessedgroove 132 is formed by dicing process corresponding to the outsidediameter of the jacket 121. This is because of enhancing the adhesiveproperties of the jacket 121 and the optical fiber 120 to the substrate130 in consideration of the flowing pressure of resin during thetransfer molding.

[0157] As material for the lead frame 150, a Cu alloy is used since theoutput of the optical device 110 is higher than the optical element 10.Inner leads 152-1 to 8 are embedded in the package 140, and outer leads153-1 to 8 are taken out outside the package 140. The outer leads 153-6and 7 are electrically connected to the optical device 110 through awiring 133 and wires 170, 170. The outer leads 153-4 and 5 areelectrically connected to the optical device 111.

[0158] The package 140 is constituted by comprehensive transfer moldingthe optical devices 110, 111, the optical fiber 120, the jacket 121, thesubstrate 130 and the lead frame 150. The package 140 is formed from a8-pin dual in-line package (DIP), whose sizes are such that for example,length is 13 mm (including length of 3.4 mm of the fiber holderportion), width is 6.3 mm, height is 3 mm, outer lead pitch is 2.54 mmand lead width is 300 mil.

[0159] The reason why the package of the second embodiment is short ascompared with the first embodiment is that in the first embodiment, theoptical fiber 20 is fixedly secured to the U groove 42 of the package40, whereas in the second embodiment, the jacket 121 is fixedly securedto the recessed groove 132 of the substrate 130 so that the package 140is sealed by transfer molding. This is because that in the firstembodiment, the package 40 is sealed by the cap 80, and in the secondembodiment, the package 140 is sealed by transfer molding.

[0160] Transfer molding material for the package 140 comprises a blackthermosetting epoxy resin. In the second embodiment, a low temperaturesetting and low thermal expansion epoxy resin was used. This is becauseof considerations that the resin molten during molding directly touchesthe jacket 121, and that after molding, the resin covers arround theoptical devices 100, 110 and the fiber 120. The elastic modulus of thisresin is 13 GPa, and the coefficient of thermal expansion is 9 ppm/° C.

[0161] The epoxy resin is transfered under compression into the moldfrom the gate portion 146 on the conditions that the plunger pressure is8 MPa, and the molding cycle time is 90 seconds to thereby mold thepackage 140. The gate portion 146 is present opposite to the fiberholder portion 141, and the flowing direction 147 of the epoxy resin inthe mold is generally parallel with the optical axis direction 123 ofthe fiber 120. It is noted that care is taken to arrangement of anejector pin of a mold so that when the module is removed from the mold,surplus stress is not applied to the optical device and the fiber.

[0162] Prior to the transfer molding, the transparent resin 160 isdropped on the optical devices 110, 111 and the portion not protected bythe jacket 121 of the bare fiber 120 to thermally set them. As materialfor the transparent resin 160, a silicone resin having a hardnesssomewhat higher than that of the transparent resin 60 in the firstembodiment was selected in a range in which the thermal stress to theoptical devices 110, 111 and the fiber 120 pose no problem. This isbecause of preventing the transparent resin 160 from being deformed inthe flowing direction 147 of resin during the transfer molding. Therefractive index of the transparent resin 160 is substantially the sameas that of the fiber 120, which is useful for improvement in the opticalcoupling characteristic and prevention of reflection of the fiber end.

[0163] Next, the assembly steps of the optical module 100 according tothe second embodiment will be explained schematically. The steps 1 to 5,7, 9 and 10 of the second embodiment corresponds to the steps 2 to 6, 9,11 and 12 of the first embodiment.

[0164] (1) The markers for the optical devices 110, 111 and thesubstrate 130 are recognized by an infrared ray image to effectalignment thereof.

[0165] (2) The load force is applied to the optical devices 110, 111,which are temporarily pressed to the substrate 30 preheated. And, anAu—Sn solder is caused to reflow, and the optical devices 110, 111 aresubjected to die bonding to the substrate 130.

[0166] (3) The substrate 130 is fixedly secured to the die pad 151 by aelectro-conductive (high heat conductive) epoxy resin.

[0167] (4) A portion between the optical devices 110, 111 and the wiring133 of the substrate 130 and a portion between the wiring 133 and theinner leads 152-4 to 7 are subjected to bonding by wires 170, 171.

[0168] (5) The extreme end of the optical fiber 120 and the extreme endof the jacket 121 are fixedly secured to the V groove 131 and therecessed groove 132, respectively, by a ultraviolet curable resin or athermosetting resin so that a spacing between the forward end of theoptical device 110 and the end of the optical fiber 120 assumes apredetermined distance.

[0169] (7) The transparent resin 160 is dropped on the optical devices110, 111 and the optical fiber 120 to heat-set it.

[0170] (8) The lead frame 150 is set to the mold, and the package 140 issubjected to transfer molding and sealed. In this case, as previouslydescribed, it is important that the direction for introducing the resinbe substantially parallel with the optical axis direction of the opticalfiber.

[0171] (9) A dam bar (not shown) or a tie bar (not shown) of the leadframe 150 is cut to bend the outer leads 153-1 to 8 into a predeterminedshape.

[0172] In this manner, the assembly of the module 100 is completed.Normally, in this stage, the predetermined inspection of characteristicsand reliability is carried out.

[0173] In the optical module 100 of the second embodiment where theresin is transferred with compassion into the mold to form the package140, as compared with the case where the resin is flown into the moldform to form a package by the casting injection method, the moldingcycle time is shortened to prevent voids in the package and to carry outmolding with accuracy. Accordingly, there is the effect that theproductivity of the module 100 is enhanced, and the quality inconnection with the shape, the reliability and so on is stabilized.

[0174] Since in the second embodiment, when the package 140 is molded,the flowing direction 147 of the epoxy resin is parallel with theoptical axis direction 123 of the fiber 120, the resin flows along thefiber 120 and the jacket 121. Accordingly, since the flowing pressure ofthe resin is not applied at right angles with the fiber 120 or thejacket 121, the fiber 120 or the jacket 121 is not distorted in theperpendicular direction, and molding will not be performed in the statein which alignment between the optical device 110 and the fiber 120 isdeviated.

[0175] Further, since the optical devices 110, 111 and the fiber 120 areprotected by the transparent resin 160, the flowing pressure is notapplied directly thereto, and the internal stress is dispersed aftermolding. Further, since in the second embodiment, no hollow portion likethe cavity 44 in the first embodiment is present, the rigidity of thepackage 140 is high. Furthermore, since the coefficient of thermalexpansion (9 ppm/° C.) of the package 140 is relatively low, the thermalstress applied to the fiber 120 is small. Accordingly, there are effectsthat it is possible to prevent the deterioration of the optical devices110, 111 and the optical fiber 120 due to the flowing pressure duringmolding and the external stress and thermal stress after molding, andthe optical output from the optical fiber 120 can be stabilized.

[0176] It is noted that there is no significant difference in the resultof measurement of optical output fluctuation before and after transfermolding and after temperature cycle test as compared with the testresult of the first embodiment, but both the embodiments show the stressresistance for a long period of time.

[0177] In connection with the moisture resistance in the secondembodiment, double sealing is made by the transparent resin 160 which isdropped or the optical devices 110, 111 and the optical fiber 120 andthe resin subjected to transfer molding. Further, as compared with thefirst embodiment, the second embodiment is large in effect ofsuppressing the immersion of water arriving at the surfaces of theoptical devices 110, 111 and the fiber 120 from the outside of thepackage. This is because the package 140 subjected to transfer moldingin the second embodiment has no hollow portion as in the resin case typepackage 40 in the first embodiment, and the resin thickness in thesecond embodiment is large as compared with the first embodiment.

[0178] However, depending on the thermal expansion difference betweenthe transparent resin 160 and the epoxy resin constituting the package140 and the adhesive properties of them, a water film is sometimesformed in the interface therebetween, but the moisture resistance posesno problem. This is because since the adhesion of the transparent resin160 with respect to the optical devices 110, 111 and the optical fiber120 is good, the water film is not formed in the interface between thetransparent resin 160, the optical devices 110, 111 and the fiber 120even under the saturated vapor pressure of the transparent resin 160.Accordingly, the second embodiment has the effects that the corrosion ofthe optical devices 110, 111 and the rupture of the fiber 120 can beprevented, and the moisture resistance can be secured. This effect hasbeen verified by the high temperature high moisture operating testsimilar to the first embodiment.

[0179] Comparing the second embodiment with the first embodiment withrespect to the cost, since the second embodiment has no cap 80 as in thefirst embodiment, as a consequence of which the number of assembly stepsin the second embodiment is less than the first embodiment by the steps(7) and (9) thereof. However, as compared with the injection molding ofthermoplastic resin in the first embodiment, the transfer molding by thethermosetting resin in the second embodiment is long in molding cycletime, and requires the cure after molding, increasing the quantity ofmaterials used. Further, it is necessary for the second embodiment tomake the substrate 130 thicker than the first embodiment and to use theheat resistant jacket 121.

[0180] Comparing with respect to the package sizes, the secondembodiment is advantageous in the following two points. That is, (1)since an adhesive interference as in the first embodiment need not beprovided, miniaturization can be achieved. (2) Since the cap need not befitted, the shape accuracy can be enhanced.

[0181] Comparing with respect to the heat dissipation, since the secondembodiment has no hollow portion as in the first embodiment, a heatconductive capacity is large, and the heat resistance can be reduced byabout 10 to 20 percent.

[0182] The selection of the first embodiment or the second embodiment inthe concrete production is determined in total consideration ofinvestment in molding/assembly equipment, conponent procuring method,specification of characteristics and reliability of opticaldevice/fiber/module, and so on.

[0183] While in the second embodiment, the low temperature setting andlow thermal expansion epoxy resin has been used as the transfer moldingresin, it is to be noted that the composition of the base resin can beadjusted according to the desired properties to combine a filler and aelasticizer. For example, the base resin includes an epoxy resin or asilicone resin; the filler includes a silica filler or a syntheticfiller; and the elasticizer includes a silicone oil or a siliconerubber. In the case where in molding, deformation of an optical fiberand a wire is reduced, a low viscosity and low speed molding resin issuitable, and in the case where a thermal stress after molding isreduced, a low elasticity and low thermal expansion resin is suitable.Further, a resin requiring no cure after molding is sometimes used inorder to enhance moldability.

[0184] The gate portion for molding the second embodiment is positionedopposite to the optical fiber supporting position, but the position ofthe gate portion may be changed according to the module construction andmoldability considering that the molding resin flows along the opticalaxis of the optical fiber. As the type of gates, an under gate, a centergate, an upper gate, a separate gate and so on can be properly used.

[0185] An example in which a number of modules are taken from themolding mold will be illustrated. FIG. 2C is a plan view showing a formin a case where the module is mass-produced using a multiple lead frame.A plurality of cavities 93 and a plurality of gates 92 are provided on amold 90, and a multiple lead frame 50 is used. The plurality of cavities93 are arranged along the runner (main flowpassage of resin) 91, and themold 90 is constituted so that the optical axis is vertical with respectto the runner 91 to thereby further increase the number of modules to beobtained.

[0186] In the second embodiment, the dropping of a transparent resin 160and the resin sealing by the transfer molding are carried out. As thetransparent resin, the resin material as mentioned in the explanation ofthe first embodiment can be also used. It is also possible to coat anover-coat resin on the transparent resin 160 in order to further enhancethe moisture resistance.

EMBODIMENT 3

[0187] In the third embodiment, as a packaging method, a transfermolding method which is a comprehensive molding mold is employed. As asealing method for an optical device and a fiber, a drooping method isemployed. In transfer molding of a package, with respect to the flowingof resins from the gate portion, care is taken so that the flowingdirection is parallel with the optical axis direction of the fiber.Thereby, the ferrule is prevented from being deviated in position due tothe molding pressure to secure the processing accuracy of a receptacleportion (i.e., accuracy of connection with a connector).

[0188] The third embodiment of the present invention will be describedhereinafter with reference to FIGS. 3A and 3B. FIG. 3A is a partial planview as viewed from the top, and FIG. 3B is a partial sectional view asviewed from the side. FIGS. 3A and 3B show a receptacle type opticaltransmission module by way of a package formed by a comprehensivemolding method.

[0189] As shown in FIGS. 3A and 3B, an optical module 200 comprisesoptical devices 210, 211, an optical fiber 220, a substrate 230, acomprehensive molding type plastic package 240, and a lead frame 250.

[0190] The optical devices 210, 211 are subjected to die bonding to thesubstrate 230. The extreme end of a ferrule 221 encasing therein anoptical bare fiber 220 is fixedly secured to a V groove 231 provided inthe substrate 230, and runs into the side of a recessed groove 232likewise provided in the substrate 230. The optical device 210 and thefiber 220, and the optical device 210 and the optical device 211 areoptically coupled with each other. The extreme ends of inner leads 252-1to 8 of the lead frame 250 are fixedly secured to the surface of thesubstrate 230. Of outer leads 253-1 to 8, 253-4 to 7 are electricallyconnected to the optical devices 210, 211 through inner leads 252-4 to 7and a wire 270. The outer leads 253-2 and 253-7 are connected to eachother through a bus bar 251. The surfaces of the optical devices 210 and211 and the side of the fiber 220 are encapslated by a transparent resin260. A receptacle portion 241 of the package 240 is provided with alatch 248 and a recessed portion 242. At the rear end of the ferrule 221projecting from the recessed portion 242, a sleeve 222 is fitted.

[0191] The specifications of the optical devices 210, 211, the fiber220, the substrate 230, the lead frame 250 and the package 240 generallycorrespond to the components used in the first or the second embodiment.

[0192] The third embodiment is different from the first or the secondembodiment in the following various points: (1) The receptacle portion241 is provided on the package 240. (2) In the receptacle portion 241,the fiber 220 is supported by the ferrule 221 in order to connect anoptical connector. (3) The ferrule 221 is supported by the V groove 231and the recessed groove 232 in consideration of the force for insertingand removing a connector applied to the receptacle portion 241. (4) Theconstruction of the package 240 is possibly symmetrical in alldirections to arrange the lead frame 250 on the base plate 230 inconsideration of the same as that just mentioned above. (5) With respectto the electric characteristics, the load capacitance of the opticaldevices 210, 211 (floating capacity of the substrate 230) is reduced,and the inductance of the lead frame 250 is reduced by the bus bar 251.

[0193] Materials for the ferrule 221 comprise zirconia ceramic, glass orplastic, which is selected according to the specifications of theconnector loss and the times of connections. The outside diameter is forexample, 0.99 mm, and the inside diameter (the diameter of athrough-hole into which the fiber 220 is inserted) is for example, 126μm. The end surface of the ferrule 221 on the receptacle portion 241side is polished in order to connect a connector. A sleeve is formed ofzirconia ceramic or plastic. When a connector is connected to thereceptacle portion 241, the connector is mechanically gripped by a latch248, and a ferrule on the connector side is inserted into a sleeve 222so that said ferrule comes in close contact with the ferrule 221.

[0194] The width of the V groove 231 of the substrate 230 is forexample, 1201 μm, which is considerably wide as compared with the Vgrooves 31, 131 in the first and the second embodiments. Because ofthis, a half-value total angle of a far field pattern of the opticaldevice 210 is narrowed down to 20×25°0 (approximately 1.4×1.1 μm in spotsize) taking the etching accuracy of the V groove 231, the outside andinside diameter-accuracy of the ferrule 221 into consideration. Therecessed groove 232 functions as a stopper of the ferrule 221, an dicingprocess is applied so that a spacing between the forward end of theoptical device 210 and the end of the ferrule 221 assumes apredetermined distance.

[0195] The length of the package 240 is 14 mm including the receptacleportion 241, the width is 6.3 mm, and the height is 3 mm. As a moldingmaterial for the package 240, an epoxy resin material having an adequateelastic modulus is used so that the latch 248 of the receptacle portion241 may be a spring function.

[0196] In transfer molding of the package 240, care is taken so that theresin is flown in the direction of arrow 247 from the gate portion 246so as to make the flowing direction 247 parallel with the optical axisdirection 223 of the fiber 220. Thereby, the ferrule 221 is preventedfrom being deviated in position due to the molding pressure to securethe processing accuracy of the receptacle portion 241 (that is, theconnecting accuracy with the connector). Since the optical devices 210,211 is surrounded by the bus bar 251 and covered by the transparentresin 260, the molding pressure is not applied directly thereto. The busbar 251 functions as a flow-stop dam when the transparent resin 260drops, and has the effect of preventing the transparent resin 260 frombeing deformed by the molding pressure.

[0197] The receptacle type module shown in the third embodiment isadvantageous for automation when the module is mounted on a print wiringsubstrate or the like. This is because the pigtail fiber need not behandled, as compared with the pigtail type module as in the firstembodiment and the second embodiment.

EMBODIMENT 4

[0198] The fourth embodiment comprises an example of a resin case typepackage. For molding the resin case, an injection molding is employed.For sealing optical devices and an optical fiber, a potting method usinga low elastic resin is used. In the injection molding, the flowing ofresin from a gate portion is in the optical axis direction of the fiber.Accordingly, since the rigidity of the package is enhanced, and thethermal expansion and thermal shrinkage are reduced in that direction,the thermal stress from the outside applied to the fiber and ferrule canbe suppressed.

[0199] The fourth embodiment of the present invention will be describedhereinafter with reference to FIGS. 4A and 4B. FIGS. 4A and 4B show areceptacle type light receiving module by way of a resin case typepackage. FIG. 4A is a partial plan view as viewed from the bottom, andFIG. 4B is a partial sectional view as viewed from the side.

[0200] As shown in FIGS. 4A and 4B, a package 340 encases therein anoptical device 311, an IC device 312, a fiber 320, and a substrate 330,which are sealed by potting of a transparent resin 360.

[0201] The optical device 311 and the IC device 312 are subjected to diebonding to the substrate 330. The extreme end of the bare fiber 320 isfixedly secured to a V groove 331 provided in the substrate 330, and theoptical device 311 and the optical fiber 320 are optically coupled. Therear portion of the optical fiber 320 is supported by a ferrule 321. Theferrule 321 is fixedly secured to a recessed groove 332 of the baseplate 320 and a U groove 342 of the package 340. A receptacle portion341 of the package 340 is provided with a latch 348 and a U groove 343,and a sleeve 322 is fitted to the ferrule 321 at the U groove 343.

[0202] A die pad 351 and wirings 352-1 to 7 are plated on the surface ofa cavity 344 in the lower surface of the package 340, terminals 353-1 to8 are plated on the recessed portion of the side, and the surface of anupper cavity 349 is also plated. Ground terminals 353-1, 3, 5, 7 and 8are connected to the die pad 351 and the wirings 352-1, 3, 5 and 7. Apower terminal 352-2, a signal terminal 352-4, and a power terminal352-6 are connected to a bias electrode of the optical device 311, asignal electrode of the IC device 312, and a power electrode of the ICdevice 312, respectively, through a wiring 333 and wires 370, 371 formedon the substrate 330.

[0203] The optical device 311 comprises a photodiode, and the IC device312 comprises a receiving circuit including a pre-amplifier foramplifying a photo current signal of the optical device 311. Thespecification of the fiber 320, the ferrule 321, the sleeve 322, and thesubstrate 330 corresponds to that described in the first to the thirdembodiments.

[0204] The fourth embodiment is different from the third embodiment inthe following points:

[0205] (1) The package 340 is a resin case having the cavities 344, 349in both upper and lower surfaces thereof.

[0206] (2) The wirings 352-1 to 7 and the terminals 353-1 to 8 areplated to thereby omit the lead frames (which teaches to be LCC type).

[0207] (3) The bare fiber 320 is fixedly secured to the V groove 331,and the ferrule 321 is fixedly secured to the recessed groove 332 andthe U groove 342 in consideration of the force for inserting andremoving the optical connector with respect to the receptacle portion341 and the thermal stress of the package 340.

[0208] The sizes of the module 300, that is, the package 340 are asfollows: The length is 16.5 mm (including the receptacle portion 341),the width is 6.3 mm, and the height is 2.8 mm. The module 300 is mountedon a separate construction (for example, such as a printed board, ahousing, etc.) with the back of the substrate 330 directed upward. Sincea part of the separate construction can be used as a cap, the number ofparts can be reduced, and the module 300 can be made to be a thin typeas compared with the first embodiment.

[0209] The terminals 353-1 to 8 are excellent in high frequencycharacteristic since they are short as compared with the lead frames asin the first to the third embodiment. Further, with respect to thewirings formed on the surface of the cavity 349, electromagnetic noisescan be shielded by the ground wirings. Further, a bypass capacitor isconnected between the ground wiring and the power wiring whereby a powersupply can be stabilized. The photodiode mounted on the receiving moduledoesn't cause a problem of heat dissipation, but in the case where alaser diode or the like is mounted in place of the optical device 311 inthe fourth embodiment, a heat sink or radiation fins may be mounted onthe cavity 349.

[0210] The package 340 is obtained by injection-molding a liquid crystalpolymer, and forming a Cu or Au plating pattern on the surface thereof.In the injection molding, the resin is caused to flow in the directionof arrow 347 from a gate portion 346. Thereby, the rigidity of thepackage 340 is enhanced in the optical axis direction 323 of the fiber320, and the thermal expansion and the thermal shrinkage are reduced,thus enabling the suppression of the thermal stress from the outsideapplied to the fiber 320 or the ferrule 321. Since the rigidity of alatch 348 can be secured, no snapping (breakage) due to the repetitionof connector connection to the receptacle 341 occurs.

[0211] For the transparent resin 360 for coating the optical device 311,the IC device 312, and the bare fiber 320, silicone rubber harder thanthe silicone gel as in the first embodiment is used. This is because thetransparent resin also serves as a sheathing material for the lowersurface of the package 340. In the case where a stray light entering theoptical device 311 through the transparent resin 360 poses a problem,the surface of the transparent resin 360 may be colored, or a blackover-coating may be applied.

[0212] While the optical modules in the first to the fourth embodimentsaccording to the present invention have been described, it is to benoted that the most important point of the present invention is thatirrespective of the fact that the plastic package is the resin case typeor the comprehensive molding type, the flowing direction of the moldresin is parallel with the optical axis of the fiber. Thereby, it ispossible to realize the lower cost and higher reliability relative tothe optical device and the optical fiber peculiar to the optical module.

EMBODIMENT 5

[0213] In the present embodiment, an example of a card type opticalmodule will be explained, in which a resin case type is used for amethod of manufacturing a resin case member.

[0214]FIG. 5 is a perspective view showing an example of the card typeoptical module. In a base 440 of the resin case member for supportingthe whole optical module are mounted module elements and connectingportions with respect to an electric system. An optical communicationsystem, a photoelectric conversion element portion and a drivingintegrated circuit portion thereof are arranged in the card type on asubstrate 430.

[0215] Mounted components corresponding to the card type as descriedabove has the constitution and characteristics basically similar tothose shown previously except employment of the form provided for thecard type.

[0216] An optical light emitting device 410 (for example, a laser diode)and an optical light receiving device 411 (for example, a photodiode)are subjected to bonding to the mounted substrate 430, which areoptically coupled by a bare fiber 420 and an optical branch waveguideportion 434. The bare fiber 420 is covered with a jacket 421. The jacket421 is supported by a fiber holder 441. These optical light receivingdevices 410, 411 are covered with the transparent resin 460. It is notedthat FIG. 5 shows only the plane area covering the transparent resin. Asemiconductor integrated circuit device 412 comprises a driving circuitof the light receiving device 410, and a semiconductor integratedcircuit device 413 comprises a light receiving circuit including apre-amplifier for amplifying a photocurrent from the light receivingdevice 411. The respective semiconductor integrated circuit devices 412,413 are mounted on a printed board 490 and connected to an externalelectric signal circuit by means of an electric connecting terminal 491and a connector 492. The printed board 490 and the connector 492 areembedded in a base 440 (which includes also a fiber holder 441) for theresin case member. Although omitted in FIG. 5, a cap of the card type ofthe resin case member is prepared to cover the base 440.

[0217] The method for manufacturing a resin case member is a “resin casetype”, which is basically similar to the first embodiment. The base 440of the resin case member and the cap are formed of a liquid crystalpolymer of a glass fiber-reinforced grade of a thermoplastic resin. Theflowing direction in molding thereof is substantially parallely with theoptical axis direction of the optical fiber. In this manner, a molecularchain of the liquid crystal polymer is oriented substantially parallelwith the optical axis direction of the optical fiber. Thereby, it ispossible to enhance the elastic modulus in the direction of the base 440of the resin case member and the cap and to reduce the coefficient ofthermal expansion. Normally, the tensile stress in the optical axisdirection or the bending stress is applied particularly to the fiberholder portion. However, in the present embodiment, the sufficientmechanical strength can be secured, and the external stress applied tothe optical fiber 421 can be suppressed.

[0218] Needless to say, the methods mentioned in the embodiments 1 to 4can be applied to the manufacturing of the card type optical module.

EMBODIMENT 6

[0219] In the present embodiment, a typical example of the opticalcommunication system will be explained. FIG. 6 is a view showing thetypical example of the optical communication system. In an opticalcommunication system 500, reference numeral 501 designates a server; 510a transmission device; 502 an optical fiber; 503 an optical distributor;520 to 523, respectively receiving devices; and 550 to 553, respectivelytransmissions to terminals. Information from the server 501 istransmitted to a plurality of terminals by the optical distributor 503.It is noted that the transmission device 510 mainly comprises atransmission LSI (integrated circuit device) portion 511, and an opticaltransmission module 512 for converting an electric signal into light totransmit it. On the other hand, each of the receiving devices 520 to 523mainly comprises optical receiving modules 530 to 533, and receiving LSI(integrated circuit device) portions 540 to 543 for photoelectricconverting light therefrom. The respective communication devicesaccording to the present invention are concerned with the constitutionof a transmission device or receiving device.

[0220] As the optical transmission module or the optical receivingmodule, the optical module illustrated in the embodiment 1 was used. Theoptical modules illustrated in the embodiments 2 to 4 can be also used.

[0221] As described above, according to the present invention, it ispossible to provide an optical communication system which has a highreliability and is inexpensive.

INDUSTRIAL APPLICABILITY

[0222] The present invention can be used for a resin mold type opticalmodule and an optical fiber communication apparatus particularly usingthe resin mold type optical module. Further, the present invention canbe applied to an optical communication system.

1. An optical module comprising an optical device, an optical fiberoptically coupled to said optical device, and a resin case member havingat least said optical device and said optical fiber mounted thereon,wherein the direction along an optical axis of said optical fiber, isthe direction of a high elastic modulus in the resin material at a mainportion along at least said optical axis of said optical fiber in saidresin case member.
 2. An optical module comprising an optical device, anoptical fiber optically coupled to said optical device, and a resin casemember having at least said optical device and said optical fibermounted thereon, wherein the direction along an optical axis of saidoptical fiber, is the direction of a low coefficient of thermalexpansion in the resin material at a main portion along at least saidoptical axis of said optical fiber of said resin case member.
 3. Anoptical module comprising an optical device, an optical fiber opticallycoupled to said optical device, and a resin case member having at leastsaid optical device and said optical fiber mounted thereon, a mainflowing direction of the resin being substantially parallel with theoptical axis of said optical fiber.
 4. An optical module comprising anoptical device, an optical fiber optically coupled to said opticaldevice, and a resin case member having at least said optical device andsaid optical fiber mounted thereon, wherein at a main portion along atleast an optical axis of said optical fiber in said resin case member,the orientation of a molecular chain of the resin is substantiallyparallel with the optical axis of said optical fiber.
 5. An opticalmodule comprising an optical device, an optical fiber optically coupledto said optical device, and a resin case member having at least saidoptical device and said optical fiber mounted thereon, wherein saidresin case member is formed of a thermoplastic resin, and the directionalong an optical axis of said optical fiber, is the direction of a highelastic modulus in the resin material at a main portion along at leastthe optical axis of said optical fiber of said resin case member.
 6. Anoptical module comprising an optical device, an optical fiber opticallycoupled to said optical device, and a resin case member having at leastsaid optical device and said optical fiber mounted thereon, wherein saidresin case member is formed of a thermoplastic resin, and the directionalong an optical axis of said optical fiber is the direction of a lowthermal expansion coefficient in the resin material of a main portionalong at least the optical axis of said optical fiber in said resin casemember.
 7. An optical module comprising an optical device, an opticalfiber optically coupled to said optical device, and a resin case memberhaving at least said optical device and said optical fiber mountedthereon, wherein said resin case is formed of a thermoplastic resin, andwhen the resin case is formed, the resin case is molded so that a mainflowing direction of the resin is substantially parallel with an opticalaxis of said optical fiber.
 8. An optical module comprising an opticaldevice, an optical fiber optically coupled to said optical device, and aresin case member having at least said optical device and said opticalfiber mounted thereon, wherein at a main portion along at least anoptical axis of said optical fiber in said resin case member, anorientation of a molecular chain of the resin is substantially parallelwith the optical axis of said optical fiber.
 9. The optical moduleaccording to any one of claims 1 to 8 , wherein said optical device andat least a portion of said optical fiber are encapsulated with atransparent resin.
 10. An optical module comprising an optical device,and an optical fiber optically coupled to said optical device, wherein amain flowing direction of the resin is substantially parallel with anoptical axis of said optical fiber to mold the resin, and then saidresin is solidified to package said optical device and at least a partof said optical fiber.
 11. The optical module according to claim 10 ,wherein said resin comprises a thermosetting resin.
 12. The opticalmodule according to any of claims 10 and 11, wherein said optical deviceand the part of said optical fiber is encapsulated on a predeterminedmember with a transparent resin, a main flowing direction of the resinis substantially parallel with an optical axis of said optical fiber tomold the resin, and then said resin is solidified and packaged,including at least said predetermined member.
 13. A method formanufacturing an optical module comprising an optical device and anoptical fiber optically coupled to said optical device, comprising thesteps of: making a main flowing direction of the resin substantiallyparallel with the optical axis of said optical fiber to mold the resin;and then solidifying said resin to package a part of said optical deviceand at least a portion of said optical fiber.
 14. The method formanufacturing an optical module according to claim 13 , wherein saidoptical device and the part of said optical fiber is coated on apredetermined member with a transparent resin, a main flowing directionof the resin is substantially parallel with an optical axis of saidoptical fiber to mold the resin, and then said resin is solidified andpackaged, including at least said predetermined member.
 15. A method formanufacturing an optical module comprising the steps of: preparing atleast an optical device, an optical fiber optically coupled to saidoptical device, a substrate having said optical device and said opticalfiber mounted thereon, and a lead frame electrically connected to saidoptical device; and flowing a thermosetting resin generally parallelywith an optical axis of said optical fiber to effect transfer moldingwith inserting said substrate and said lead frame.
 16. An opticalcommunication apparatus comprising at least an optical module and anassembly substrate on which said optical module is mounted, said opticalmodule having at least an optical device, an optical fiber opticallycoupled to said optical device, and a package encasing said opticaldevice and at least a part of said optical fiber, said package being apackage molded by flowing a resin substantially parallely with theoptical axis of said optical fiber.
 17. An optical communicationapparatus comprising at least an optical module and an assemblysubstrate on which said optical module is mounted, said optical modulehaving at least an optical device, an optical fiber optically coupled tosaid optical device, and a package encasing therein said optical deviceand at least a part of said optical fiber, the direction of along anoptical axis of said optical fiber being the direction of high elasticmodulus in the resin material at a main portion along at least theoptical axis of said optical fiber in said package.
 18. An opticalcommunication apparatus comprising at least an optical module and anassembly substrate on which said optical module is mounted, said opticalmodule having at least an optical device, an optical fiber opticallycoupled to said optical device, and a package encasing therein saidoptical device and at least a part of said optical fiber, the directionof along an optical axis of said optical fiber being the direction of alow thermal expansion coefficient in the resin material at a mainportion along at least the optical axis of at least said optical fiberin said package.
 19. An optical communication apparatus comprising atleast an optical module and an assembly substrate on which said opticalmodule is mounted, said optical module having at least an opticaldevice, an optical fiber optically coupled to said optical device, and apackage encasing therein said optical device and at least a part of saidoptical fiber, the direction of along the optical axis of said opticalfiber being the direction of orientation of a molecular chain in theresin material at a main portion along at least said optical axis of atleast said optical fiber in said package.